Digital Bioacoustics

Birdsong is one of the most beautiful sounds on the planet, but did you know that those tweets and calls have a complex 'sentence' struture that could tell us a lot about the evolution of human language?

When composer Emily Doolittle was given the chance to spend time at the Max Planck Institute for Ornithology in Germany, the birds she heard became her inspiration.

Doolittle wove together the sounds of partridges, geese and wrens in a piece she titled Seven Duos for Birds or Strings, first performed in 2014.

"Many birds use similar timbres, pitch relationships and patterns to human music," she says. "I think there is lots of room for musicians and scientists to work together to better understand animal songs."

Like Doolittle, researchers around the world are increasingly exploring links between birdsong and human sounds. We may be far apart on the evolutionary tree (scientists estimate the last common ancestor of birds and mammals may have lived more than 300 million years ago), but humans nevertheless happen to have a lot in common with birds when it comes to making themselves heard. The musician wren, for example, which features in Doolittle’s work, is native to the Amazon and has inspired music across South America. As Doolittle found, the wren sings using the same intervals found frequently in human music – octaves, perfect fifths and perfect fourths.
Meaning behind the music

But do beautiful birdsong and chirping calls contain more than melody? Is there a deeper complexity that affects the meaning? Toshitaka Suzuki and his colleagues at The Graduate University for Advanced Studies in Japan certainly think so. They’ve found that Japanese tits can arrange the calls they make in order, like words in a sentence, with the arrangement of calls changing the overall meaning – a system known as syntax. The rules of syntax in human language relate to the structure of a sentence, and the order in which we say words. It’s why we would say ‘I’m going to the shops,’ rather than ‘the shops to I’m going,’ for example.

"Tits are known for having these very complicated call systems – a lot of the calls in the Japanese tit repertoire have meanings," explains David Wheatcroft at Uppsala University in Sweden, who also worked on the Japanese study. One call refers to predatory snakes, for instance, and another to the danger of hawks overhead. Parents also have different calls for their chicks, telling them to flee or duck in the face of danger. What is special about Japanese tits is that they seem able to combine at least two of these calls together.

The researchers learnt that there was one particular combination that prompted birds to scan for a predator and then also to approach and harass it. Like human syntax, this combination only worked if the tits’ calls were uttered in a particular order.

"Syntax was considered to have uniquely evolved in humans, but our study demonstrates that it has evolved in a wild bird, too. I think many basic features of language capacity are shared between humans and non-human animals, including birds," says Suzuki. According to Wheatcroft, songbirds such as the Japanese tit may even provide a new model for studying the evolution of syntax.

Linguist Moira Yip at University College London welcomes such exciting new work into animal communication, but points out that tits’ capabilities are limited when compared to what humans can do.

"They have found a system that has two “words”, and one combination, and at the moment that is it," she says. "We, on the other hand, can combine any adjective and any noun to make a new phrase… so from only 10 adjectives and 10 nouns we can create a hundred two-word phrases."

"In evolutionary terms, birds are extremely distant relatives of humans," she adds. Even so, the way birds learn their songs does show some parallels with the way humans acquire language – for example, the way we use syllables and stress certain sounds in a rhythmic way. "Birdsong has internal structure that is reminiscent of the way human speech groups sound," says Yip.
Honeyed tones

However far apart we are from birds in terms of evolution, most of us love birdsong. Bird watchers often learn to imitate their calls, and a few societies have built a dialogue with the birds around them. In parts of Africa, honey gatherers connect with a bird known as the honeyguide, which helps them track down bees’ nests.

"People walk through the bush making special sounds to alert honeyguides. The Yao people of Mozambique make one particular sound in this context," says evolutionary biologist Claire Spottiswoode at the University of Cambridge, who has studied them. It’s like a trill followed by a grunt, she says.

‘Talking’ to the birds like this doubles the odds that a honeyguide will help search for a bees’ nest.

"It tells the honeyguide you’re their friend," one honey gatherer told her. This system brings many benefits. For the hunter-gatherer Hadza community in Tanzania, as much as a tenth of their calories comes from the honey they collect. In return, the birds feed on the wax after the humans have taken the honey.

"The interaction between humans and honeyguides is likely to be very ancient, probably something in the order of hundreds of thousands of years," adds Spottiswoode. While tame animals often interact with their owners, honeyguides are wild, making this relationship unique. "Their cooperative behaviour has almost certainly evolved through natural selection," she says.

Research such as this highlights that birds aren’t as ‘bird-brained’ as some people had assumed. Indeed, in 2016, European and South American researchers studying two-dozen species found that, while birds’ brains may be relatively tiny, the cells within them can be more densely packed than those of rodents and some primates. Parrots and songbirds have some of the most surprising brains of all.

"We probably underestimated how many species have some communication system," says Moira Yip. "Nevertheless, the gulf between human language and the systems found in birds, cetaceans and even primates remains huge, and how that gulf was crossed as humans evolved remains largely mysterious."

Even so, bird researchers continue to be surprised by the likenesses they see between humans and birds, especially in making a tune.

"There is no common ancestor of birds and humans that had a music-like song," says Doolittle. "But somehow, independently through evolution, birds and humans have ended up fairly similar, both in the way they sound and in the role songs play in their lives."